If $\sum_{i=1}^\infty a_i$ diverges, then prove that $\sum_{i=1}^\infty ia_i$ diverges.
My English is too bad to express the question clearly. Thank you for your answer.
If $\sum_{i=1}^\infty a_i$ diverges, then prove that $\sum_{i=1}^\infty ia_i$ diverges.
My English is too bad to express the question clearly. Thank you for your answer.
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